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Öğe Effect of supporting electrolyte on capacitance and morphology of electrodeposited poly(3,4-propylenedioxythiophene) derivatives bearing reactive functional groups(Royal Soc Chemistry, 2022) Sarac, Baran; Karazehir, Tolga; Gilsing, Hans-Detlev; Eckert, Juergen; Sarac, A. SezaiThe interactions between the electrolyte and electroactive species in redox active PProDOT derivatives can be enhanced with better-performing electrodes for electrochemical energy conversion and storage. Differently functionalized 3,4-propylenedioxythiophenes (ProDOTs) are electropolymerized from acetonitrile using Et4NBF4, Et4NPF6, or NaClO4 as an electrolyte to evaluate the electrochemical performance of the considered polymer derivatives, as well as under monomer-free conditions. We propose a new equation to assess the kinetics of the diffusion-limited adsorption process with two independent solved parameters: diffusion slope k and power exponent b. Electron-donating groups attached to the monomer stabilize radical cation and dication formation during electrogrowth. The ProDOT-Br structure has a low oxidation potential owing to the electron-rich group in the heterocyclic structure, which grants access to a radical cation intermediate and interaction with the ions of the electrolyte. Surface roughness and morphology are assessed by atomic force microscopy and scanning electron microscopy, respectively. The changes in the Fourier transform infrared spectrum are more pronounced with the selection of electrolyte type than the type of derivatives. Except the -OBz derivative, the largest specific capacitance calculated from the area under the final cyclic voltammetry curves is obtained for Et4NBF4, followed by Et4NPF6 and NaClO4. In all systems, the -OPhCH2OH derivative exhibited the lowest electrolyte diffusion. More pronounced diffusion is observed for the PProDOT derivatives measured in Et4NPF6 and Et4NBF4 electrolytes, whereas the lowest diffusion is obtained for the NaClO4 electrolyte. Findings in this study provide new insights into the factors requiring attention upon tailoring assemblies for organic electronic applications.Öğe Effective electrocatalytic methanol oxidation of Pd-based metallic glass nanofilms(Royal Soc Chemistry, 2020) Sarac, Baran; Karazehir, Tolga; Ivanov, Yurii P.; Putz, Barbara; Greer, A. Lindsay; Sarac, A. Sezai; Eckert, JuergenCompared to their conventional polycrystalline Pd counterparts, Pd79Au9Si12 (at%) - metallic glass (MG) nanofilm (NF) electrocatalysts offer better methanol oxidation reaction (MOR) in alkaline medium, CO poisoning tolerance and catalyst stability even at high scan rates or high methanol concentrations owing to their amorphous structure without grain boundaries. This study evaluates the influence of scan rate and methanol concentration by cyclic voltammetry, frequency-dependent electrochemical impedance spectroscopy and a related equivalent circuit model at different potentials in Pd-Au-Si amorphous NFs. Structural and compositional differences for the NFs are assessed by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray (EDX) mapping and X-ray diffraction (XRD). The ratio of the forward to reverse peak current density i(pf)/i(pb) for the MG NFs is similar to 2.2 times higher than for polycrystalline Pd NFs, evidencing better oxidation of methanol to carbon dioxide in the forward scan and less poisoning of the electrocatalysts by carbonaceous (e.g. CO, HCO) species. Moreover, the electrochemical circuit model obtained from EIS measurements reveals that the MOR occurring around -100 mV increases the capacitance without any significant change in oxidation resistance, whereas CO2 formation towards lower potentials results in a sharp increase in the capacitance of the Faradaic MOR at the catalyst interface and a slight decrease in the corresponding resistance. These results, together with the high i(pf)/i(pb) = 3.37 yielding the minimum amount of carbonaceous species deposited on the thin film during cyclic voltammetry and stability in the alkaline environment, can potentially make these amorphous thin films potential candidates for fuel-cell applications.Öğe Effective Methanol Oxidation with Platinum Nanoparticles-Decorated Poly(2-bromomethyl-2-methyl-3,4-propylenedioxythiophene)-Coated Glassy Carbon Electrode(Electrochemical Soc Inc, 2021) Karazehir, Tolga; Sarac, Baran; Gilsing, Hans-Detlev; Eckert, Juergen; Sarac, A. SezaiHere, we developed a porous network of bromomethyl-substituted 3,4-propylenedioxythiophene polymer using a simple and efficient technique of electrochemical deposition used as conductive support for methanol oxidation. Platinum nanoparticles (PtNPs) are well dispersed and decorated on a high surface area of electrochemically deposited Poly(2-bromomethyl-2-methyl-3,4-propylenedioxythiophene (PProDOT-Br) on a glassy carbon electrode (GCE). A thin film of PProDOT-Br acts as a supporting matrix for deposition of PtNPs and improves the interfacial properties between electrode and electrolyte. The PtNPs-decorated PProDOT-Br (Pt/PProDOT-Br) samples were characterized by X-ray diffraction, Fourier transform infrared attenuated total reflectance spectroscopy, atomic force microscopy, and scanning electron microscopy. Furthermore, the electrocatalytic performance of Pt/PProDOT-Br on GCE for methanol oxidation was assessed by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy measurements. The findings suggest that the use of Pt/PProDOT-Br/GCE assemblies for efficient methanol oxidation in alkaline media with a small intermediate poisoning is promising for applications as anode material in DMFCs, which should be attributed to the PProDOT-Br support providing a larger surface area with porous nature and enabling the adsorption of more CH3OH for further oxidation. The developed porous network PProDOT-Br with high capacitance may also have large potential in supercapacitor applications.Öğe Electrocatalytic Behavior of Hydrogenated Pd-Metallic Glass Nanofilms: Butler-Volmer, Tafel, and Impedance Analyses(Springer, 2020) Sarac, Baran; Karazehir, Tolga; Muehlbacher, Marlene; Sarac, A. Sezai; Eckert, JuergenElectrocatalytic activity and sorption behavior of hydrogen in nanosized Pd-Si-(Cu) metallic glass thin film and Pd thin film electrodes sputtered on a Si/SiO2 substrate were investigated by linear sweep voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. The electrode MG4 (Pd69Si18Cu13) exhibits the best performance with the highest electrocatalytic activity in the hydrogen evolution region with less than half of the Tafel slope of Pd thin film of the same thickness and lowest overpotential at 10 mA cm(-2). A new approach has been adopted by a nonlinear fitting of the entire region of the polarization curve (far- and near-equilibrium cathodic and anodic regions) to the Butler-Volmer model. a parameter is lowest for the MG2 electrode (Pd79Si16Cu5), marking that nonequilibrium conditions change the reaction kinetics. Together with MG2, MG4 shows the lowest Bode magnitude values for hydrogen sorption and evolution regions, indicating that the bonding and release of hydrogen atoms to the electrode is easier. MG4 electrode shows a dramatic decrease of the overpotential after 100 cycles, yielding an increase in hydrogen activity. Besides, MG4 exhibits the sharpest current density drop in the HER region in cyclic voltammetry compared with other MG and Pd electrodes, indicating higher electrocatalytic activity towards hydrogen evolution. The findings highlight the influence of the selected metallic glasses for the design and development of metal catalysts with higher sorption kinetics and/or electrocatalytic turnover.Öğe Electrosorption of Hydrogen in Pd-Based Metallic Glass Nanofilms(Amer Chemical Soc, 2018) Sarac, Baran; Karazehir, Tolga; Muehlbacher, Marlene; Kaynak, Baris; Gammer, Christoph; Schoeberl, Thomas; Sarac, A. SezaiAs an efficient potential hydrogen storage and conversion system, hydrogen electrosorption and evolution mechanisms in Pd-based metallic glass thin films (MGTFs) are investigated. In this study, thin films of 55 nm thickness were deposited by dc magnetron sputtering. The amorphous structure of MGTFs and the atomically smooth interface between the MGTF and substrate were confirmed by transmission electron microscopy, whereas the composition-dependent surface roughness was obtained via atomic force microscopy. The shifts in the broad diffraction maxima for the Si and Cu additions were evaluated by X-ray diffraction. The Pd thin film (PdTF) and MGTF working electrodes were chronoamperometrically saturated in 0.5 M H2SO4 solution. The formation of palladium hydride (PdHx) in the MGTFs was investigated by X-ray photoelectron spectroscopy. Cyclic voltammograms were subsequently recorded (between -0.2 and 1.4 V) at sweep rates of 0.02 V s(-1). Electrochemical impedance spectroscopy of MGTFs and PdTF was performed in full spectrum including sorption, desorption, and evolution of hydrogen in a conventional three-electrode configuration. Electrochemical circuit modeling provided the relationship between the composition-dependent hydrogen evolution and H absorption/adsorption processes. The adsorption capacitance parameter Y-ad corresponding to alpha- and beta-hydride formation in the case of Pd0.79Si0.16Cu0.05 MGTF is similar to 5 times higher than that of the crystalline Pd thin film which is in line with the decrease in the charge-transfer resistance R-ct. Addition of Cu disturbs the symmetry of the glass formers, leading to remarkable changes in interfacial hydrogen bonding and diffusion of hydrogen into sublayers. Compared to other Pd-based micron-sized materials, our findings show excellent volumetric hydrogen storage capacity 4 times higher than that of the traditional counterparts of several microns, and 50% higher than the Pd thin films of the same thickness, together with high tunable capacitance, charge-transfer resistance, and diffusivity depending on the glass-forming characteristics of the nanosized MGTF.Öğe Enhancement of Interfacial Hydrogen Interactions with Nanoporous Gold-Containing Metallic Glass(Amer Chemical Soc, 2021) Sarac, Baran; Ivanov, Yurii P.; Micusik, Matej; Karazehir, Tolga; Putz, Barbara; Dancette, Sylvain; Omastova, MariaContrary to the electrochemical energy storage in Pd nanofilms challenged by diffusion limitations, extensive metalhydrogen interactions in Pd-based metallic glasses result from their grain-free structure and presence of free volume. This contribution investigates the kinetics of hydrogen-metal interactions in goldcontaining Pd-based metallic glass (MG) and crystalline Pd nanofilms for two different pore architectures and nonporous substrates. Fully amorphous MGs obtained by physical vapor deposition (PVD) co-sputtering are electrochemically hydrogenated by chronoamperometry. High-resolution (scanning) transmission electron microscopy and corresponding energydispersive X-ray analysis after hydrogenation corroborate the existence of several nanometer-sized crystals homogeneously dispersed throughout the matrix. These nanocrystals are induced by PdHx formation, which was confirmed by depth-resolved X-ray photoelectron spectroscopy, indicating an oxide-free inner layer of the nanofilm. With a larger pore diameter and spacing in the substrate (Pore40), the MG attains a frequency-independent impedance at low frequencies (similar to 500 Hz) with very high Bode magnitude stability accounting for enhanced ionic diffusion. On the contrary, on a substrate with a smaller pore diameter and spacing (Pore25), the MG shows a larger low-frequency (0.1 Hz) capacitance, linked to enhanced ionic transfer in the near-DC region. Hence, the nanoporosity of amorphous and crystalline metallic materials can be systematically adjusted depending on AC- and DC-type applications.Öğe Functionalized highly electron-rich redox-active electropolymerized 3,4-propylenedioxythiophenes as precursors and targets for bioelectronics and supercapacitors(Royal Soc Chemistry, 2021) Karazehir, Tolga; Sarac, Baran; Gilsing, Hans-Detlev; Gumrukcu, Selin; Eckert, Jurgen; Sarac, A. SezaiIn order to combine capacitive properties with processability, e.g. solubility in organic solvents, poly(3,4-propylenedioxythiophene) derivatives containing different functional groups like oxyphenyl methanol (-OPhCH2OH), oxybenzyl (-OBz), bromide (-Br) and tosyl (-OTs) were synthesized and electropolymerized as thin films from acetonitrile (ACN) using Et4NBF4 as an electrolyte. Multifunctionality in the substitution pattern of the polymer exhibits a similar trend between monomer oxidation potentials and specific capacitance (C-sp) vs. crystal size. The presence of pi-pi stacking interactions in the polymer structures plays an important role in building the crystal structures. The same order of flat band potential and C-sp values are observed for -OBz < -Br < -OTs < -OPhCH2OH substitutions. The structures of PProDOT-OBz and PProDOT-OPhCH2OH resemble each other much more than those of PProDOT-Br and PProDOT-OTs. Impedance measurements were conducted at different applied biases in order to define a Mott-Schottky analysis revealing the dependence of the semiconducting properties on the type of substituent present in the PProDOT derivative.Öğe Metallic Glass Films with Nanostructured Periodic Density Fluctuations Supported on Si/SiO2as an Efficient Hydrogen Sorber(Wiley-V C H Verlag Gmbh, 2020) Sarac, Baran; Ivanov, Yury; Karazehir, Tolga; Putz, Barbara; Greer, A. Lindsay; Sarac, A. Sezai; Eckert, JuergenNanostructured metallic glass films (NMGF) can exhibit surface and intrinsic effects that give rise to unique physical and chemical properties. Here, a facile synthesis and electrochemical, structural, and morphologic characterization of Pd-Au-Si based MGs of approximately 50 nm thickness supported on Si/SiO(2)is reported. Impressively, the maximum total hydrogen charge stored in the Pd-Au-Si nanofilm is equal to that in polycrystalline Pd films with 1 mu m thickness in 0.1 mH(2)SO(4)electrolyte. The same NMGF has a volumetric desorption charge that is more than eight times and 25 % higher than that of polycrystalline PdNF and Pd-Cu-Si NMGF with the same thickness supported on Si/SiO2, respectively. A significant number of nanovoids originating from PdH(x)crystals, and an increase in the average interatomic spacing is detected in Pd-Au-Si NMGF by high-resolution TEM. Such a high amount of hydrogen sorption is linked to the unique density fluctuations without any chemical segregation exclusively observed for this NMGF.Öğe Multilayer crystal-amorphous Pd-based nanosheets on Si/SiO2 with interface-controlled ion transport for efficient hydrogen storage(Elsevier Ltd, 2022) Sarac, Baran; Ivanov, Yurii P.; Karazehir, Tolga; Mühlbacher, Marlene; Sarac, A. Sezai; Greer, A. Lindsay; Eckert, JürgenThis contribution shows an unusually high hydrogen storage of multilayer amorphous (A)-crystalline (C) Pd–Si based nanosheets when stacked in the right order. Samples with A/C/A/C/A stacking sequence exhibit 40 and 12 times larger hydrogen sorption than monolithic crystalline and amorphous samples, respectively. The maximum capacitance calculated from the fitting of electrochemical impedance measurements of the same sample is twice larger than that of the conventional polycrystalline Pd films of similar thickness. Five times higher diffusion coefficient calculated from modified Cottrell equation is obtained compared to specimens with C/A/C/A/C stacking. For the A/C/A/C/A multilayers, nanobubbles with diameters of 1–2 nm are homogeneously distributed at Si/SiO2 interface, and PdHx crystal formation in these regions confirms hydrogen-metal interactions. Furthermore, corrosion-resistant amorphous top layer permits larger amounts of hydrogen ion transfer to inner layers. Thus, hydrogen storage and production can be enhanced by smart design of multilayers targeted for proton exchange membrane electrolysis or fuel cells. © 2021 Hydrogen Energy Publications LLCÖğe Nanoporous Pd-Cu-Si Amorphous Thin Films for Electrochemical Hydrogen Storage and Sensing(Amer Chemical Soc, 2021) Sarac, Baran; Karazehir, Tolga; Yuce, Eray; Muehlbacher, Marlene; Sarac, A. Sezai; Eckert, JuergenIncreasing the efficiency of hydrogen storage and release using recent generation metallic glass nanofilms (MGNFs) offers green solutions for nanoscale energy applications. Contrary to flat nanofilms, enhanced electrochemical performance of Pd-Cu-Si MGNF assemblies for hydrogen interaction is obtained on different sizes and configurations of a nanoporous alumina support. In particular, 10 nm thick samples with pore diameters of 25 nm reach a high specific pseudocapacitance per unit mass of 637 F g(-1), which is more than an order of magnitude larger than for flat samples, surpassing the precious metal-based systems in the literature. The same electrode exhibits the highest double-layer capacitance calculated from the equivalent circuit model of the electrochemical impedance spectra, featuring its eligibility for hydrogen nanosensors. A rough and fully coated surface is attained for samples of 250 mu m thickness and above, while smoother and open-pore structures are observed for lower thicknesses, inducing a capillary pressure and turbulent flow effect for the latter case. The comparison of cyclic voltammetry (CV) profiles recorded in the region where hydrogen-metal interactions occur confirms a remarkable desorption charge difference, reaching 2.5 times higher values for the 50 nm thick 25 nm pore diameter than the 40 nm pore diameter and flat electrodes, and lower absolute impedance values near-DC range revealing their highly conductive behavior.Öğe Oligoether Ester-Functionalized ProDOT Copolymers on Si/Monolayer Graphene as Capacitive Thin Film Electrodes(Electrochemical Soc Inc, 2020) Karazehir, Tolga; Sarac, Baran; Gilsing, Hans-Detlev; Eckert, Juergen; Sarac, A. SezaiIn this study, electrochemical polymerization of 3,4-propylenedioxythiophene (ProDOT 1), ProDOT bearing oligoether ester (ProDOT-EO-ester 2) and their copolymerization onto homogeneously CVD coated nano-graphene/Si support is realized to attain graphene/ProDOT based copolymer hybrid nanostructures. By introducing oligoether side chain to ProDOT backbone and using different [ProDOT]/[ProDOT-EO-ester] molar ratios ensures a considerable decrease in oxidation potential of polymer allowing tunable properties to copolymers revealing improvement electrochemical capacitance and electrochemical activity which are clearly reflected by the experimental results. Capacitive behavior of copolymers is determined by electrochemical impedance spectroscopy, cyclic voltammetry. Moreover, The structural, morphological and spectroscopic characterization of the copolymers is investigated by XRD, AFM, SEM, EDX, FTIR, and Raman, respectively. By the increase of ProDOT in the copolymer composition, the higher dopant concentration is attained suggesting an enhanced conductivity agree well with the impedance and CV results, where the copolymerization of ProDOT 1 and ProDOT-EO-ester 2 in equal molarity results in the highest specific capacitance and redox activity. The adopted equivalent circuit model for polymers is in good agreement with the experimental data of impedance. Due to the difference in conjugated structure between ProDOT and ProDOT-EO-ester by the presence of the EO-ester group leads to a decrease in charge transfer resistance with increasing mole fraction of ProDOT-EO-ester. The charge transfer resistance of [ProDOT](0)/[ProDOT-EO-ester](0) = 1:1 coated Si/graphene is nearly 51 and 24 times lower value compared to those of PProDOT and P(ProDOT-EO-ester) homopolymers coated Si/graphene, respectively, confirming that the copolymerization improves the electron conduction. By Mott-Schottky measurements, increasing mole fraction of ProDOT-EO-ester 2 in copolymer composition results in the alteration of semiconducting behavior. The developed graphene-polymer hybrid electrodes can be a potential candidate for energy storage devices. (C) 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.Öğe Origin of Electrocatalytic Activity in Amorphous Nickel-Metalloid Electrodeposits(American Chemical Society, 2021) Sarac, Baran; Karazehir, Tolga; Micusik, Matej; Halkali, Celine; Gutnik, Dominik; Omastova, Maria; Sarac, A. SezaiIn transition metal-based alloys, the nonlinearity of the current at large cathodic potentials reduces the credibility of the linear Tafel slopes for the evaluation of electrocatalytic hydrogen activity. High-precision nonlinear fitting at low current densities describing the kinetics of electrochemical reactions due to charge transfer can overcome this challenge. To show its effectiveness, we introduce a glassy alloy with a highly asymmetric energy barrier: amorphous NiP electrocoatings (with different C and O inclusions) via changing the applied DC and pulsed current and NaH2PO2 content. The highest hydrogen evolution reaction (HER) activity with the lowest cathodic transfer coefficient ? = 0.130 with high J0 = -1.07 mA cm-2 and the largest surface areas without any porosity are observed for the pulsed current deposition. The calculated ? has a direct relation with morphology, composition, chemical state and coating thickness defined by the electrodeposition conditions. Here, a general evaluation criterion with practicality in assessment and high accuracy for electrocatalytic reactions applicable to different metallic alloy systems is presented. © 2021 American Chemical Society.Öğe Peripherally and non-peripherally carboxylic acid substituted Cu(ii) phthalocyanine/reduced graphene oxide nanohybrids for hydrogen evolution reaction catalysts(Royal Soc Chemistry, 2023) Kaplan, Ekrem; Karazehir, Tolga; Gumrukcu, Selin; Sarac, Baran; Sarac, A. Sezai; Hamuryudan, EsinDue to growing environmental concerns and increasing energy needs, hydrogen, one of the key options as a future energy carrier, has lately gained more interest. In this study, we have reported nanohybrid electrocatalyst materials based on peripherally and non-peripherally carboxylic acid substituted copper phthalocyanines (CuPcs) and reduced graphene oxide (rGO) constructed via pi-pi interactions between CuPcs and rGO. Prepared nanocomposites were coated onto the surface of a glassy carbon electrode and their electrocatalytic activity for the hydrogen evolution reaction (HER) was studied. Structural, electrochemical, and surface morphological properties of the produced electrodes were investigated using Fourier transform infrared (FT-IR) and Raman spectroscopy, X-ray diffraction (XRD), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) analyses. Electrochemical measurements indicated that the peripherally substituted rGO/CuPc electrodes have more efficiency and activity compared to the non-peripherally substituted ones. In addition, the EIS results show that peripherally carboxylic substituted rGO/CuPc electrodes become more conductive due to the position and content of the carboxyl groups. This increasing performance of the HER implied by a smaller impedance together with more facile electron transfer kinetics indicates a pronounced enhancement of the electrocatalytic hydrogen activity of peripherally carboxylic substituted rGO/CuPc electrodes.Öğe Surface-governed electrochemical hydrogenation in FeNi-based metallic glass(Elsevier, 2020) Sarac, Baran; Zadorozhnyy, Vladislav; Ivanov, Yurii P.; Kvaratskheliya, Askar; Ketov, Sergey; Karazehir, Tolga; Gumrukcu, SelinThe hydrogenation and oxide formation behavior of Fe-Ni-based metallic glasses (MGs), where measurements by the conventional gas-solid reaction method are difficult, is analyzed by a two-step approach: chronoamperometry followed by cyclic voltammetry (CA + CV). We introduce a concept of effective volume by measuring the thickness of the region where the hydrogen and hydroxyl ion interactions with Fe-based MG take place, which is characterized by high-angle annular dark-field scanning transmission electron microscopy. A very constant film thickness influenced by the OH- and H+ is confirmed by TEM, where the chemical homogeneity is maintained within this region. The weight percent of hydrogen and the corresponding hydrogen-to-metal ratio are determined as 1.16% and 0.56, respectively. When compared to previous studies conducted by the electrochemical- permeation method, the H/M ratio is found to be an order of magnitude larger. Electrochemical impedance spectroscopy (EIS) and subsequent equivalent circuit modeling (ECM) of the tested ribbons resolve the surface-diffusion processes for hydride formation and oxidation kinetics. This contribution provides a different perspective for the design and study of low-cost and high-performance amorphous nanofilms for hydrogenenergy applications, particularly when the common gas-adsorption methods are problematic.Öğe Synergistic enhancement of hydrogen interactions in palladium-silicon-gold metallic glass with multilayered graphene(Royal Soc Chemistry, 2023) Sarac, Baran; Ivanov, Yurii P.; Putz, Barbara; Karazehir, Tolga; Mitterer, Christian; Greer, A. Lindsay; Sarac, A. SezaiAmorphous PdSiAu-based metallic glass thin films (MGTFs) obtained by physical vapor deposition were deposited on multilayered graphene (MLGR) supported on Si/SiO2, where the MLGR is carried to the top by upward pressure of the deposited atomic layer passing through the crystal lattice of graphene. Samples were electrochemically hydrogenated by chronoamperometry and characterized by cyclic voltammetry in 0.1 M H2SO4. MLGR-containing samples have a prominent Raman peak at 1415 cm-1. This sample shows & SIM;2.6 times larger hydrogen desorption charge and & SIM;4.5 times larger electrocatalytic hydrogen activity compared to the MLGR-free counterparts. Furthermore, the capacitance retrieved from the simulation of electrochemical impedance data indicates a & SIM;2.6 times increase upon MLGR inclusion. High-resolution (scanning) transmission electron microscopy after hydrogenation corroborates the existence of nm-sized PdHx crystals around the MGTF-Si/SiO2 interface and the presence of a graphene layer on top of the MGTF due to bond breaking between the MLGR and Si/SiO2. The enhanced hydrogen activity due to the synergistic effect of MLGR and MGTF layer-by-layer nanostructure reveals itself in the diffusion kinetics, where 50% faster hydrogen ion transfer into the MGTF is obtained when the MLGR top layer is present. The areal and volumetric hydrogen desorption charge exceed almost all the considered Pd-based counterparts, especially when comparing systems with similar thicknesses. Hence, the developed hybrid nanostructure can be envisaged as an alternative ultra-high hydrogen charger for small-scale applications. Presence of only a few layers of graphene boosts hydrogen intake of Pd-based metallic glass thin films by 2.6 times with 4.5 times higher electrocatalytic hydrogen evolution reaction activity, a tremendous improvement in metal-hydrogen interactions.Öğe Ultrahigh hydrogen-sorbing palladium metallic-glass nanostructures(Royal Society of Chemistry, 2019) Sarac, Baran; Ivanov, Yurii P.; Karazehir, Tolga; Mühlbacher, Marlene; Kaynak, Baris; Greer, A. Lindsay; Sarac, A. SezaiPd-Based amorphous alloys can be used for hydrogen energy-related applications owing to their excellent sorption capacities. In this study, the sorption behaviour of dc magnetron-sputtered and chronoamperometrically-saturated Pd-Si-Cu metallic-glass (MG) nanofilms is investigated by means of aberration-corrected high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy, and electrochemical techniques. The volume expansion of ?V = 10.09 Å3 of a palladium hydride unit cell obtained from HRTEM images due to the hydrogenation of the Pd-MG nanofilms is 1.65 times larger than ?V of the Pd-polycrystalline counterpart loaded under the same conditions. Determined by scanning transmission electron microscopy-high annular dark-field imaging and electron energy loss spectroscopy, the huge difference between the two Pd-based systems is accounted for by the "nanobubbles" originating from hydrogenation, which generate active sites for the formation and expansion of spatially dispersed palladium hydride nanocrystals. A remarkable difference in the hydrogen sorption capacity is measured by electrochemical impedance spectroscopy compared to the Pd polycrystal nanofilms particularly in the ? and ? regions, where the maximum hydrogen to palladium ratio obtained from a combination of chronoamperometry and cyclic voltammetry is 1.56 and 0.61 for the MG and Pd-polycrystal nanofilms, respectively. The findings place Pd-MGs among suitable material candidates for future energy systems. © The Royal Society of Chemistry.
